Preparing lithographic plates utilizing hydrolyzable mercapto-silane compounds

ABSTRACT

It has been found that lithographic printing plates can be prepared by (a) photografting to an unsaturated oleophilic organic polymer substrate a potentially hydrophilic hydrolyzable mercapto-silane compound having the general formula   WHERE R is an organic radical, X is selected from mono and dialkylamino, alkyl and aryl amido, alkoxy, aryloxy and alkyl and aryl oxycarbonyl radicals; T is selected from alkyl, cycloalkyl, aryl, alkaryl and aralkyl radicals, and the corresponding halogenated radicals; a is an integer from 1 to 3; b is an integer from 0 to 2; c is an integer from 1 to 3; and a+b+c equals 4; (b) washing away non-photografted mercapto-silane compound; and (c) amplifying the hydrophilicity of the hydrolyzable silane groups by treating with a soluble silicate solution or a colloidal silica dispersion.

United StattBS Patent n91 Boardman et al.

[ Sept. 23, 1975 PREPARING LITI-IOGRAPI-IIC PLATES UTILIZINGHYDROLYZABLE MERCAPTO-SILANE COMPOUNDS [73] Assignee: HerculesIncorporated, Wilmington,

Del.

[22] Filed: June 27, 1974 [21] Appl. No 483,845

Primary Examiner-Norman G. Torchin Assistant Examiner-Judson R.l-lightower Attorney, Agent, or Firm-Marion C. Staves [57] ABSTRACT Ithas been found that lithographic printing plates can be prepared by (a)photografting to an unsaturated oleophilic organic polymer substrate apotentially hydrophilic hydrolyzablc mercapto-silane compound having thegeneral formula where R is an organic radical, X is selected from monoand dialkylamino, alkyl and aryl amido, alkoxy, aryloxy and alkyl andaryl oxycarbonyl radicals; T is selected from alkyl, cycloalkyl, aryl,alkaryl and am]- kyl radicals, and the corresponding halogenatedradicals; a is an integer from 1 to 3; b is an integer from 0 to 2; c isan integer from I to 3; and a+b+c equals 4; (b) washing awaynon-photografted mercapto-silane compound; and (c) amplifying thehydrophilicity of the hydrolyzable silane groups by treating with asoluble silicate solution or a colloidal silica dispersion.

7 Claims, N0 Drawings PREPARING LITHOGRAPHIC PLATES UTILIZINGHYDROLYZABLE MERCAPTO-SILANE COMPOUNDS This invention relates to a novelmethod for preparing lithographic printing plates, More particularly,this invention relates to a method for preparing lithographic printingplates by imagewise photochemically grafting a mercapto-silane compoundto an oleophilic organic polymer substrate, washing away non-graftedcompound, and then amplifying the hydrophilicity of the hydrolyzable orhydrolyzed silane groups.

It is known to modify the surface of various hydrophilic substrates byphotocrosslinking imagewise a thin layer of resin coated on thesubstrate. After washing away the uncrosslinked resin, the resultingplate consists of oleophilic crosslinked resin printing areas, andhydrophilic substrate non-printing areas.

It has now been found that lithographic printing plates of excellentquality can be prepared by (l) photografting image-wise to anunsaturated oleophilic organic polymer substrate a potentiallyhydrophilic hydrolyzable mercapto-silane compound, (2) washing awaynongrafted mercapto-silane compound, and (3) amplifying thehydrophilicity of the hydrolyzable silane groups by treating with asoluble silicate solution or a colloidal silica dispersion. Byphotografting is meant the direct photoinitiated chemical couplingreaction of a mercapto-silane compound with an organic polymer. Byamplifying the hydrophilicity" is meant reacting the graftedhydrolyzable or hydrolyzed silane groups with soluble silicates orcolloidal silica thus greatly in creasing the hydrophilic character ofthe grafted sites.

Any unsaturated organic polymer can be used as the substrate inaccordance with this invention, provided it is oleophilic, wettable byorganic solvent-based inks,

but is insoluble in and substantially unswollen by such inks. Mostamorphous polymers with a second order transition temperature belowabout 50C. must be crosslinked to some degree to provide such solventresistance. Typical applicable polymers are unsaturated hydrocarbonpolymers including trans-1,4- polybutadiene, trans-l ,4-polyisoprene,cyclized natural rubber, unsaturated rubbers such as buty rubber,natural rubber, styrene-butadiene rubber, cis-l,4- polyisoprene,1,2-polybutadiene, and ethylene-. propylene-dicyclopentadieneterpolymer, and blends of these polymers with each other ornon-hydrocarbon polymers.

in addition to the hydrocarbon polymers, a large number of otherunsaturated polymers and modified unsaturated polymers, includingcopolymers, terpolymers, etc., may be used. Typical of these otherpolymers are unsaturated cellulose derivatives such as allyl ethermodified cellulose acetate and ethyl cellulose;

drying alkyd resins; allyl pentaerythritol derivatives where R is anorganic radical, X is selected from mono and dialkyl amino, alkyl andaryl amido, alkoxy. aryloxy and alkyl and aryl oxycarbonyl radicals; Tis selected from alkyl, cycloalkyl, aryl, alkaryl and aralkyl radicalsand the corresponding halogenated radicals; where, most preferably, thealkyl groups will contain 1 to 18 carbon atoms, the cycloalkyl groupswill contain 5 to 8 carbon atoms, and the aryl groups will contain 1 to2 rings; a is an integer from 1 to 3; I; is an integer from 0 to 2; c isan integer from 1 to 3; and a+b+c equals 4. Most preferably, R will bean organic radical selected from the group consisting of alkylene,cycloalkylene, arylene, alkarylene, aralkylene, alkyl diarylene,

aryl dialkylene, alkyl dicycloalkylene, cycloalkyldialalkylene-oxy-alkylene, arylene-oxy-arylene, alkarylene-oxy-arylene,alkarylene-oxy-alkarylene, aralkylene-oxy-alkylene, andaralkylene-oxyaralkylene; as well as the corresponding halogenatedradicals; where the alkyl and alkylene groups will contain 1 to 18carbon atoms, the cycloalkyl and cycloalkylene groups will contain 5 to8 carbon atoms, and the aryl and arylene groups will contain 1 to 2rings. Typical mercapto-silane compounds are kylene,

8-mercaptopropyl trimethoxysilane S-mercaptopropyl tributoxysilancB-mercaptopropyl trichlorobutoxysilane fi mereaptopropyltrioctadecoxysilane S-mercaptopropyl triheptoxysilane a-mercaptotolyldimethylaminophenylsilane a-mercaptotolyl bis(dimethyl aminomethylsilancContinued CHg-CH-z HS-CH B-( p-mcrcaptophenyl )cthyldiphenoxyphcnylsilunc /3( p-mercaptophenyl )ethyldiphcnoxynaphthylsilune B-( 4-mcrcaptocyclohexyl ethyl triacctoxysilaneB-( B-mercaptocyclopentyl ethyl triaeetoxysilane' B-(S-mercaptocyclooctyl)ethyl trimethoxysilaneB-mcrcaptoethoxyethyltricthoxysilane 4-mercaptohutyltriisoprnpoxysilanc4-mercaptomethyl-4 '-trimethoxysilane diphenyl etherS-mercaptobutyldimethylmethoxysiluneS-mercaptbdichlorobutyldimethylmethoxysilane bis( p-mercaptophenyl)dimethoxysilane tris( p-mercaptophenylethyl methoxysilane tris(acetamido )--y-mercuptopropylsilane tris(N-methylbenzamido-y-mercaptopropylsilane bis(-y-mercaptopropyl)dimelhoxysilane tris('y-mercupt0propyl )methoxysilane I ing whenirradiated with light can be used as a photoinitiator. Typical of thesedyes are thionine, eosin, phlox ine, rose bengal, hematoporphyrin,erythrosine, acriflavine, benzoin methyl ether, benzophenone, Michlersketone, thioxanthone, and the like. The amount of pho- 1 toinitiatorwill depend upon the specific photoinitiator being used. However, theamount will preferably be sufficient to absorb substantially all of theincident radiation at the wave length of the maximum absorption of thephotoinitiator.

The oleophilic organic polymer substrate can be coated with the silanecompound in a number of ways. as for example, by dipping, brushing,rolling, etc., a solution or dispersion of the compound on thesubstrate. Typical solvent for the silane compounds are methanol,methylene chloride, acetone, methyl ethyl ketone or combinations of suchsolvents with water. Since the silane groups are to be amplified, it isonly necessary to coat with a very thin layer of silane compound. Mostpreferably, at least about moles per cm will be used.

The amount and type of light radiation required to initiate graftingwill vary, depending upon the silane compound being grafted and thephotoinitiator being used. In general, photografting can be completed ina few seconds to minutes. Photografting of mercaptosilanes willpreferably be carried out with, but is not limited to use of, visiblelight. The optimum period of time and optimum wave length range ofradiation required to initiate photografting using any particular silanecompound can readily be determined by one skilled in the art.

Non-grafted silane compound can be removed from unexposed areas bywashing with a solvent with or without scrubbing or brushing. Suitablesolvents for removing the unreacted silane compound depend on the natureof the compound, but typically would be the same type as used to applythe compound. If water is present during the washing stage, hydrolyzablegroups of the reacted silane will be hydrolyzed at this stage.

As pointed out above, the hydrolyzable or hydrolyzed silane groups onthe photografted silane compound are treated with a silicate solution ora colloidal silica suspension to amplify their hydrophilicity. Anywater-soluble silicate including both alkali and quaternary ammoniumsalts, can be used, as well as any silica which can form a colloidalsuspension. In some cases it may be desirable to use a mixture ofsilicate and colloidal silica. There is not a definite distinctionbetween soluble silicates and colloidal silicas, the difference betweenthe two classes being arbitrary. Soluble silicates range from the alkalimetal orthosilicates (2M O'SiO M alkali metal), sesquisilicates (3MO-2SiO and metasilicates (M O-SiO through higher molecular weightpolysilicates with high average SiO /M O ratios. As the SiO /M O ratioincreases, aqueous solutions become more viscous. At still higherratios. the silicates give the typical opalescence and bluish cast dueto light scattering. The system can, at this point, be considered anaqueous colloidal dispersion of discrete particles of surfacehydroxylated silica. The choice of alkali metal, pH, and concentrationof added aluminum oxide or other chemical modifiers affects the SiO /M Oratio at which a true colloid may be said to exist. When a colloid isformed, the SiO /M O ratio is so high that the bulk of the amorphousmasses which have formed is largely SiO The surface of the particles aremade up of -SiOH and "SiOM functionality. The positive ions are insolution. The charge layers at each particle surface repel one another,stabilizing the sol. Soluble and colloid silicates can also be preparedwith other monovalent positive counter ions in addition to the alkalimetals, for example, quaternary ammonium salts, such astetraethanolammonium and tetraethylammonium silicates, and otherammonium derivatives. Typical alkali metal silicates are sodiumsilicate, potassium silicate, lithium silicate. Typical commercialcolloidal silicas are Ludox HS-40, HS, LS, SM-30. TM, AS, and AM (E. l.duPont). These materials vary in colloidal particle size. pH,stabilizing ion, SiO /M O ratio, etc.

The silicate or silica amplifying agents can be applied to thepreviously photografted surfaces by a number of methods. By one methodthe photografted polymer plate is merely soaked in a silicate solutionor colloidal suspension of silica. Soaking for a period of from about 1minute to as much as several hours at a temperature from roomtemperature to about C. will generally be sufficient. Other methods byapplying the silicate or silica amplifying agents are by wiping,brushing or pouring the solution or suspension onto the plate surface.The amount of amplifying agent applied will be sufficient to react withall the silane groups photografted on the polymer substrate. In general,solutions of silicates or suspensions of colloidal silica will containfrom about 1% to about 40%, by weight of amplifier.

Periodic retreatment of the plate after use may also be desirable torestore the hydrophilic properties.

As demonstrated in the working examples, the preparation of lithographicplates by the claimed photografting and amplification process offersseveral advantages. First, the process is a way of making positiveworking lithographic plates. Second, expensive and toxic organicsolvents are not required in the developing step. Third, the quality ofthe plate can be renewed after use or storage.

The following examples are presented for purposes of illustration, partsand percentages being by weight unless otherwise specified.

EXAMPLE 1 This example illustrates hotografting an alkyl mercaptosilaneto a crosslinked unsaturated polyester resin substrate and thenamplifying with a silicate.

A 5 mil grained aluminum lithographic plate is coated, using a Meyer rodwith 6 mil wire, with an anhydrous Cellosolve acetate solutioncontaining 57.5 parts of the Cellosolve acetate. 30 parts of a polyesterresin, prepared from fumaric acid and the diol made by condensingpropylene oxide with Bisphenol A, and having a molecular weight ofapproximately 3000, l l .5 parts of a trifunctional isocyanatecrosslinking agent, the reaction product of 3 moles of hexamethylenediisocyanate and lmole of water, named as the biuret of hexamethylenediisocyanate, and composed principally of a compound believed to havethe structure:

and 1 part of zinc acetate. The thus coated plate was cured in an aircirculating oven for 1 hour at a temperature of C.

A 0.1 molar methanol solution of gamma-mercaptopropyl trimethoxysilanehaving the formula and containing by weight of phloxine dye (based onthe mercaptosilane weight) was prepared. This solution was brushed ontothe crosslinked polyester substrate at a concentration of approximately0.1 cc. per 10 cm to give a final surface concentration of themercaptosilane of 10 moles per cm" after evaporation of the methanolsolvent.

The resulting plate was covered with a transparency held in place by aglass plate and exposed to a 650 watt visible movielight type lamp heldat a distance of 20 inches for 3 minutes. During exposure a blower wasused to cool the surface of the plate. After exposure, the plate waswashed with methanol to remove mercaptosilane from the unexposed areas.Then the plate was soaked for hours in a 26% aqueous potassium silicatesolution. After the resulting lithographic plate was washed with water,it was wiped with processing gum and inked with a lithographicdeveloping ink to render the image pattern visible. The thus imagedplate was used in a lithographic press with a conventional lithographicink and fountain solution. Over 1000 impressions were made withsatisfactory results.

EXAMPLE la This example illustrates amplification by use of a silicateat lower concentration.

A plate was prepared as in Example 1, except the amplification procedurewas modified as follows. The imaged plate was soaked in a 5% solution ofpotassium silicate for 30 minutes. The plate was run on a lithographicpress with satisfactory results.

EXAMPLE lb This example illustrates the retreatment of a,deterioratedlithographic plate with a silicate solution to restore performance.

The process of Example 1 was repeated. The resulting plate was allowedto run on a lithographic press until the hydrophilic areas began todeteriorate by scumming. The press was stopped and ink removed from theplate with solvent. The plate was then rubbed vigorously with a padsaturated with a 13% aqueous solution of potassium silicate. After 5minutes, the excess silicate solution was wiped off with a water-soakedpad. The press was restarted. The printing was satisfactory, showingthat the hydrophilic areas of the plate had been restored.

EXAMPLE 2' This example illustrates photografting an alkylmercaptosilane to a crosslinked unsaturated polyester resin substrateand then amplifying with a combination of silicate and silica.

The procedure of Example 1 was repeated except that the exposure timewas increased to 8 minutes and the soaking in potassium silicatesolution was replaced by soaking for 5 hours in a 1:1 mixture of 39%aqueous potassium silicate solution and 30% colloidal sodium ionstabilized silica dispersion (containing 30.0% SiO and 0.2% AI O with aSiO- /Na O weight ratio of 230 dispersed as l3l4 mu diameter particlesin. water). The plate was run on a lithographic press for over 3000impressions with satisfactory results.

EXAMPLE 3 This example illustrates photografting of an alkylmercapto-silane to a crosslinked polyester resin substrate and thenamplifying with an organic colloidal siltea.

The procedure of Example 1 was repeated exactly except rose bengal wasused as the sensitizing dye, and the soaking in potassium silicate wasreplaced by soaking for 5 hours in a 15% ammonium ion stabilized silicadispersion (containing l5.0% SiO with a SiO /NH weight ratio ofdispersed as 13 to .14 mp. particles in water). The plate was run on alithographic press for over 3000 impressions with satisfactory results.

EXAMPLES 4l 3 These examples illustrate photografting of an alkylmercapto-silane to a crosslinked polyester resin substrate and thenamplifying with a variety of colloidal silicas and silicates.

The procedure, of Example 3 was repeated exactly except the colloidalammonium silicate was replaced by other silicate solutions or silicadispersions.

ammonium Each plate was run on a lithographic press for over 3000impressions with satisfactory results.

EXAMPLE l4 This example illustrates photografting of an alkylmercapto-silane to a crosslinked unsaturated styrenebutadiene copolymerrubber substrate and then amplifying with a silicate. The procedure ofExample 2 was repeated except the polyester coated aluminum substratewas replaced by a 5 mil grained aluminum lithographic plate which wascoated, using a 12 mil doctor blade, with a 12% solution of a copolymerof styrene and butadiene in toluene, containing 0.5 wt. 71 (based on thepolymer) of dicumyl peroxide. The thin coated plate was cured undernitrogen in an oven at l50C5for 40 minutes. In addition, the phloxinedye was replaced with rose bengal, and exposure was for 15 minutes.After imagingand silicate amplification, the plate was run on alithographic press for over lOOOimpressions with satisfactory results. ii

Example 17 Example [8 Example 21 Example 22 Example 23 Example 24Example 25 Example 26 Example 27 Example 28 EXAMPLES 15 AND 16 Theseexamples illustrate photografting of an alkyl mercapto-silane tocrosslinked unsaturated substrates and then amplifying with a silicate.

The procedure of Example 14 was repeated except the copolymer of styreneand butadiene was replaced with (Example 15) natural rubber, and(Example 16) a terpolymer of 65 mole percent ethylene, 30 mole per--cent propylene, and 5 mole percent dicyclopentadiene. In each case theplate was run on a lithographic press for over l000 impressions withsatisfactory results.

EXAMPLES 17-28 These examples illustrate photografting of a variety ofmercapto-silanes to a crosslinked unsaturated polyester substrate andthen amplifying with a silicate.

The procedure of Example I was repeated exactly except thegamma-mercaptopropyl trimethoxysilane 20 was replaced by othermercapto-silanes:

y'mercaptopropyl triethoxysilane u-mercaptotolyl bis-(dimethylaminomethyl- CH silane) zf z B-( 4-mercaptocyclohexyl)ethyltriacetoxysilanc B-mereaptoethoxyethyL triethoxysilane4-mcrcapto3-chlorohutyltriisopropoxy- H, silane 4-mercaptomctl1yl-4'-trimethoxysilane diphenyl ether (C 3):

OCH;,

tris( acetamido )-'y-mercaptopropylsilane H lris( N-methylbenzamido)--ymcrcaptopropylsilane 1 In each example the plate was run on alithographic press for over 1000 impressions with satisfactory results.

EXAMPLE 29 This example illustrates the use of an ultraviolet sensitizerand imaging using ultraviolet light.

The procedure of Example 1 was repeated except phloxine was replacedwith Michlers ketone and the plate was imaged by exposure to a mercuryshort are lamp for two minutes. After silicate treatment, the plate wasrun on a lithographic press for over 1000 impressions with satisfactoryresults.

EXAMPLE 30 This example illustrates the use of an ultraviolet sensitizerand imaging using ultraviolet light.

The procedure of Example 1 was repeated except phloxine was replacedwith thioxanthone, and the plate was imaged by exposure to a mercuryshort are lamp for 2 minutes. After silicate treatment, the plate wasrun on a lithographic press for over 1000 impressions with satisfactoryresults.

EXAMPLES 3 l33 These examples illustrate preparation of lithographicplates by photografting an alkyl mercapto-silane to uncrosslinkedthermoplastic polymers and then amplifying with a silicate.

Five mil grained aluminum lithographic plates were laminated to 5 milsheets of the following unsaturated polymers by molding the polymers tothe sheets in a compression press: (Example 3|) trans-1,4-butadiene witha molecular weight of about 250,000; (Example 32) an allyl ethermodified ethylcellulose with a molecular weight of about 200,000 with anaverage degree of substitution of 2.5 cthoxy substituents and 0.2 allylether substituents per anhydroglucose unit; (Example 33) a crystallineepichlorohydrin allyl glycidyl ether copolymer containing a molar ratioof 90: l epichlorohydrin to allyl glycidyl ether monomer units and witha molecular weight of about 200,000.

These plates were coated with gammamercaptopropyltrimethoxysilanesolution containing phloxine dye, exposed through a transparency, washedwith methanol, soaked in potassium silicate solution, and run on alithographic press according to the procedure of Example 1(a). Theplates were run on the press for over 1000 impressions with satisfactoryresults.

What we claim and desire to protect by Letters Patent is: I

l. A process for preparing a lithographic printing plate which comprisesthe following steps:

a. photografting imagewise to an unsaturated oleophilic organic polymersubstrate a hydrolyzable mercapto-silane compound having the generalformula where R is an organic radical, X is selected from mono anddialkyl amino, alkyl and aryl amido, alkoxy, aryloxy and alkyl and aryloxycarbonyl radicals; T is selected from alkyl, cycloalkyl, aryl,alkaryl, aralkyl radicals and the corresponding halogenated radicalsj ais an integer from I to 3; b is an integer from 0 to 2; c is an integerfrom 1 to 3; and a+b+c equals 4;

b. washing away non-photografted mercapto-silane compound from unexposedareas; and

c. amplifying the hydrophilicity of the hydrolyzed silane groups bytreating with at least one amplifying agent selected from solublesilicate solutions and colloidal silica dispersions. 2. The process ofclaim 1 wherein the oleophilic organic polymer substrate is acrosslinked polyester resin. 3. The process of claim 1 wherein theamplifying agent is a silicate.

away non-photografted mercapto-silane compound from unexposed areas, theimprovement of amplifying the hydrophilicity of the silane groups on thephotografted hydrolyzed mercapto-silane compounds by treating with atleast one amplifying agent selected from soluble silicate solutions andcolloidal silica dispersions.

1. A PROCESS FOR PREPARING A LITHOGRAPHIC PRINTING PLATE WHICH COMPRISES THE FOLLOWING STEPS: A. PHOTOGRAFTING IMAGEWISE TO AN UNSATURATED OLEOPHILIC ORGANIC POLYMER SUBSTRATE A HYDROLYZABLE MERCAPTOSILANE COMPOUND HAVING THE GENERAL FORMULA
 2. The process of claim 1 wherein the oleophilic organic polymer substrate is a crosslinked polyester resin.
 3. The process of claim 1 wherein the amplifying agent is a silicate.
 4. The process of claim 1 wherein the amplifying agent is colloidal silica.
 5. The process of claim 1 wherein the amplifying agent is a mixture of silicate and colloidal silica.
 6. A lithographic printing plate prepared by the process of claim
 1. 7. In a process of preparing a lithographic printing plate which comprises photografting imagewise to an unsaturated oleophilic organic polymer substrate a hydrolyzable mercapto-silane compound and washing away non-photografted mercapto-silane compound from unexposed areas, the improvement of amplifying the hydrophilicity of the silane groups on the photografted hydrolyzed mercapto-silane compounds by treating with at least one amplifying agent selected from soluble silicate solutions and colloidal silica dispersions. 